DESCRIPTION (APPLICATION ABSTRACT): The Institute of Medicine (IOM) estimated that medical errors result in more than a million injuries and between 44,000 and 98,000 deaths each year. Physicians' working conditions may be an important contributing factor to the frequency and severity of iatrogenic errors. Hospital residents traditionally work 30- to 38-hour on-call shifts every two-to-four nights for months at a time, with work hours ranging from 80 to 110 hours a week. Laboratory and field data indicated that such extended duty shifts and long work weeks are associated with acute total sleep deprivation, chronic partial sleep deprivation, misalignment of circadian phase, and sleep inertia. These factors result in a deterioration of alertness and neurobehavioral performance of interns, which may lead to an increased risk of serious adverse events resulting in decreased patient safety. We plan to test the hypotheses that: 1) the minimum and mean duration of sleep obtained per night on-call will be significantly increased in hospital interns for whom a night float provides 10 hours of protected time for sleep during on-call nights when compared with those who are not provided night-float coverage; 2) medical error rates and the levels of subjective and objective indicators of fatigue of noncovered interns during the second half of their overnight call shifts will be significantly greater than in the same group of interns during the first half of their night-float-covered on-call shifts; and 3) patient safety, as measured by total medical errors and serious medical errors will be significantly improved by implementation of a night- float system. An intervention study is proposed to evaluate the efficacy of providing 10 hours of protected time for sleep in improving patient safety and reducing serious adverse events by alleviating alertness and performance deficits in interns associated with recurrent 30- to 38-hour on-call shifts. The proposed study should provide the evidence base on how resident work hours affect patient safety and thereby have important public policy implications related to graduate medical training of the approximately 100,000 medical and surgical residents in the United States who are the principal providers of health care in academic medical centers across America.